Exhaust system

ABSTRACT

An exhaust system for a motor vehicle internal combustion engine is described in which the lower end of the exhaust manifold (10) and the upper end of the down pipe (12a, 12b) each comprise two or more conduits which are sector shaped in cross section and are arranged to form a complete circle split by radial walls. The circumference of the down pipe is sealed by a flexible ball joint (14) against the circumference of the manifold (10) and the radial walls (16c) of the down pipe (12a, 12b) are spaced from the radial walls (10a) of the manifold by a small gap sufficient to permit pivoting of the down pipe relative to the manifold. The down pipe (12a, 12b) is urged against the manifold (10) by clamping bolts (20) the heads of which are pivotable relative to the exhaust system about an axis passing through the pivotal center of the flexible ball joint.

FIELD OF THE INVENTION

The present invention relates to an exhaust system and in particular tothe joint in an internal combustion engine between the exhaust manifoldand the down pipe.

BACKGROUND OF THE INVENTION

The engine of a motor vehicle is supported on flexible engine mounts andcan rock during operation. Because of the mass of the exhaust pipe andthe manner of its mounting on the vehicle body, rocking of the enginegives rise to significant stresses in the exhaust system which reducethe life of the system.

In order to assist in isolating the exhaust system from the rocking ofthe engine, flexible ball joints have been proposed for use at thejunction between two pipe sections. The term "flexible ball joint" isused in the present specification to a refer to a joint having a collarwith a part-spherical surface which seals between a flange on one of thepipe sections and a part-spherical seat on the other, the joint allowingthe pipe sections to pivot relative to one another without any escape ofexhaust gases.

Such a joint has been used at the lower end of the down pipe, but thereit is far removed from the rocking axis of the engine. The length of thedown pipe exaggerates the rocking and introduces considerable side toside movement, which cannot be accommodated by a single flexible balljoint.

It has also been proposed to use a flexible ball joint at the top end ofthe down pipe, where it joins on to the exhaust manifold. In this case,the down pipe has but a single conduit and it is not possible to tunethe length of the branches of the exhaust manifold to enhancescavenging.

GB-A-1 586 244 describes an exhaust system for a motor vehicle internalcombustion engine, in which the lower end of the exhaust manifold andthe upper end of the down pipe each comprise two conduits which aresector shaped in cross section and are arranged to form a completecircle split by radial walls. The circumference of the down pipe issealed by a flexible ball joint against the circumference of themanifold and the radial walls of the down pipe are spaced from theradial walls of the manifold by a small gap sufficient to permitpivoting of the down pipe relative to the manifold.

Though this exhaust system is capable of permitting the engine to rockrelative to the down pipe, the construction and design of the clampingbolts which hold the parts of the flexible ball joint against oneanother interfere with the operation of the ball joint and are a sourceof squeaks.

OBJECT OF THE INVENTION

The invention therefore seeks to provide an exhaust system in which aflexible ball joint is provided to enable the engine to rock relative toexhaust down pipe but in which the flexible ball joint is held togetherby clamping bolts which do not interfere with the function of the balljoint and do not squeak in operation.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an exhaust systemfor a motor vehicle internal combustion engine, in which the lower endof the exhaust manifold and the upper end of the down pipe each comprisetwo or more conduits which are sector shaped in cross section and arearranged to form a complete circle split by radial walls, and whereinthe circumference of the down pipe is sealed by a flexible ball jointagainst the circumference of the manifold and the radial walls of thedown pipe are spaced from the radial walls of the manifold by a smallgap sufficient to permit pivoting of the down pipe relative to themanifold, characterised in that the down pipe is urged against themanifold by clamping bolts the heads of which are pivotable relative tothe manifold about an axis passing through the pivotal centre of theflexible ball joint.

Conveniently, the exhaust manifold and the down pipe are divided intoonly two conduits by a partition wall extending along a diameter of theflexible ball joint.

A further problem found with the proposal of GB-1 586 244 is that thepivotal centre of the flexible ball joint is far removed from the rollcentre of the engine. The roll centre is usually designed to lie abovethe joint between the manifold of the down pipe and in the above priorart patent the pivotal centre of the flexible ball joint lies beneaththe joint.

In accordance with a preferred feature of the present invention, theflexible ball joint is formed by a concave part-spherical seat formed onah attachment secured to the down pipe and convex surface on a sealingcollar mounted on the manifold. Because the flexible ball joint is madeconcave upwards, instead of concave downwards, its pivotal centre isbrought closer to the roll centre of the engine.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described further, by way of example, withreference to the accompanying drawing which shows schematically thejoint in an exhaust system of the invention between the manifold and thedown pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawing, an exhaust manifold 10 is joined to a pair of down pipeconduits 12a and 12b by a flexible ball joint, described in more detailbelow, which is sealed by a collar 14. The two conduits 12a and 12b arebrought together at their upper end within a stainless steel attachment16. The attachment 16 has two sockets for receiving the conduits 12a and12b which are D-shaped when view in plan and arranged back to back todefine a full circle with a dividing wall 16c extending along adiameter.

The attachment 16 also has a flange 16d formed with holes for receivingclamping bolts 20 which hold the down pipe conduits 12a and 12b againstthe exhaust manifold 10.

The lower end of the manifold 10 when viewed from the direction of thedown pipe is likewise divided into two by a diametrically extendingdividing wall 10a aligned with the wall 16c of the attachment 16 andspaced from it by only a small clearance.

In a four cylinder engine, the exhaust gases from two of the cylinders,operating in anti-phases, will be directed to flow along one of theconduits while the gases from the other two cylinder flow along theother. The two gas flows do not meet until the lower ends of theconduits join one another. As in the case of an exhaust system withseparate joints for two down pipes, the lengths of the exhaust pipes canbe tuned in order to improve scavenging.

A single flexible ball joint secures both down pipe conduits 12a and 12bto the manifold 10. To this end, the manifold 10 has at its lower end ashoulder 10b against which there is seated the collar 14. The latter isformed of a slightly compressible material, preferably a wire mesh cladwith a layer of copper. The collar 14 is compressed between the shoulderon the exhaust manifold and a part spherical seat 16a defined by theattachment 16 and maintains a gas tight seal while permitting the downpipe conduits 12a and 12b to pivot relative to the exhaust manifold 10about the centre of the part-spherical seat 16a formed in the attachment16.

The attachment 16 and the manifold 10 are resiliently held against oneanother by means of springs 23 fitted around the two clamping bolts 20.Each clamping bolt 20 has a head 20a which can be received in a blindbore 22 in the manifold. A steel pin 24 traverses the blind bore 22 anda through cross bore 20d in the head 20a to prevent withdrawal of thehead 20a from the blind bore 22 and to define a pivot axis about whichthe attachment 16 may rock relative to the manifold. The aligned axes ofthe two pins 24 are arranged to lie on a central axis of the partspherical surface 16a at right angles to the partition walls 10a and16c. This geometry of the clamping bolts 20 permits the joint to bendwithout any change in the length of the springs 24 which assists inmaintaining the correct tension on the sealing collar 14 and in avoidingsqueaks.

To assemble the flexible ball joint, it would be possible to tighten thenuts 20b on the bolts 20 after the heads 20a have been inserted into themanifold 10 and held in place by means of the pins 24. However, to easeand speed assembly, it is preferred to pre-assemble the bolts 20 andsprings 24 on the attachment flange 16d and to hold the springscompressed by means of U-shaped clips (not shown) engaging between theflanges 16d and the heads 20a of the clamping bolts 20. After the heads20a have been retained in the manifold by insertion of the pins 24, theclips can be withdrawn, leaving the springs correctly tensioned.

It is possible to arrange the axis of the pins 24 on or very close tothe roll centre of the engine and this reduces significantly thestresses to which the exhaust pipe and the exhaust manifold aresubjected while still permitting tuning of the lengths of the manifoldbranches.

In this context, it should be noted that the roll centre of an engine isusually designed to be higher than the joint between the manifold andthe down pipe. For this reason, the flexible ball joint in the describedpreferred embodiment is convex downwards, that is towards the down pipe.In this way, the pivotal axis of the flexible ball joint lies on themanifold side of the ball joint and the heads of clamping bolts engagein the manifold 10 rather than the attachment 16.

Rocking of engine at right angles to the roll axis is also accommodatedby the flexible ball joint in that the springs 20 can be individuallycompressed during such rocking motion.

It should be mentioned that other constructions of the clamping boltsare possible which permit the bolts to pivot relative to the exhaustsystem. For example, if the manifold is provided with a flange similarto the flange 16d of the attachment 16, then the heads of the bolts andthe mating surfaces on the flange may be curved to allow the desiredpivotal movement centre on the axis of the flexible ball joint.

We claim:
 1. An exhaust system for a motor vehicle internal combustionengine, having an exhaust manifold with a lower end and a down pipe withan upper end, in which the lower end of the exhaust manifold (10) andthe upper end of the down pipe (12a, 12b) each comprise two or moreconduits which are sector shaped in cross section and wherein the downpipe is sealed against the manifold (10) by a ball joint having apivotal centre and the down pipe (12a, 12b) is spaced from the radialwalls (10a) of the manifold by a small gap sufficient to permit pivotingof the down pipe relative to the manifold, characterised in that thedown pipe (12a, 12b) is urged against the manifold (10) by clampingbolts (20) having heads which are pivotable relative to the manifoldabout an axis passing through the pivotal centre of the flexible balljoint.